Beam addressable disk drive systems, e.g. optical and magneto-optical information storage systems, typically require provision for positioning and clamping a removable and replaceable information storage disk on a spindle drive such that the central aperture of the disk is firmly held in precise coaxial relationship with the spindle axis. Precision centering of the disk relative to the spindle axis of rotation is important to minimize runout (eccentric rotation) which can unduly stress the tracking servo of the drive system.
An example of a general type of disk centering and clamping apparatus is shown in German Offenlegengschrift 29 09 099, published Sept. 11, 1980, a magnetic clamping device for a video or audio disk record player employs a free-floating ferromagnetic clamping ring mounted for axial movement in a disk receiving slot of a hinged cover. The clamping ring is held offset from the disk slot by means of a low strength magnet fixedly mounted on the upper surface of the cover. When the cover, with a disk positioned in the slot, is rotated down to place the disk on the spindle-drive, the clamping ring is attracted away from the low strength magnet toward a higher strength magnet positioned in the spindle on the other side of the disk thus clamping the disk to the spindle drive. When the cover is later opened, the clamping ring is pulled by the disk away from the spindle-drive magnet and attracted to the cover magnet thus allowing the disk to be removed from the cover. A retainer keeps the clamping ring with the cover when the cover is closed and opened with no disk in place in the cover. A constant diameter spindle post with a chamfered end is used for centering the disk as the cover is closed over the spindle-drive.
In U.S. Pat. No. 4,570,194 issued Feb. 11, 1986, a computer optical disk is inserted in a fixed slot until the disk central aperture is centered under a bistable magnetic clamp mounted in the slot cover. An axially movable, annular, non-magnetic clamping device which houses an internal annular magnet is held levitated above the disk slot within a fixed annular ferromagnetic ring. After a disk is inserted into the slot, the spindle-drive comprised of a ferromagnetic turntable is raised into engagement with the disk causing the flux from the levitated magnet to change direction from the levitating ring into the turntable drive. This, in turn, attracts the clamp to the turntable thus clamping the disk to the spindle-drive. When the spindle-drive is lowered, the flux reverts to the annular ring, levitating the clamp and allowing removal of the disk. This disclosure also relies on a constant diameter spindle post with a chamfered end to center the disk on the drive.
In both of the foregoing representative disclosures, no provision is made for assuring highly precise centering of the disk on the spindle-drive since the central aperture of the fully seated disk is positioned about the vertical surface of a constant diameter spindle post. Proper centering in this case is a function of assuring a close tolerance fit between the post and the disk aperture, at best a costly approach that can result in deteriorated performance with long term wear on the disk central aperture.
U.S. Pat. No. 4,510,592, issued Apr. 9, 1985, is representative of improved centering arrangements in the art in which the disk central aperture is centered on the frustro-conical surface of a centering member mounted on the spindle-drive. In this patent, a video disk is placed on a spindle-drive and a clamping device placed over the spindle. The spindle-drive includes a spring loaded, frustro conical centering member which is mounted for axial movement on the spindle inside the circumference of a disk drive turntable which is also mounted on the spindle. An independent, spring-loaded stabilizing ring is positioned between the centering member and turntable to hold the disk parallel to the turntable surface as the disk is being centered by the member in the process of clamping the disk to the turntable. A magnet in the centering member cooperates with a ferromagnetic coupler ring in the clamping device to hold the disk firmly on the turntable. Any tolerance or wear variations in the diameter of the disk central aperture are accommodated by the spring loading of the centering member which assures positive seating of the disk on the turntable drive surface with full contact by the disk aperture around the conical surface of the centering member. In this disclosure, the disk and clamping device apparently are both manually inserted on the spindle-drive. As a consequence, the user can visually determine that the disk is correctly placed on the conical surface of the centering member before placing the clamping device on the spindle.
It is known to protect sensitive surfaces of optical and magneto-optical disks by enclosing the disks in protective cartridges. In order to permit free rotation of the disk in the cartridge, the internal cavity of the cartridge is significantly larger than the disk, although a retaining mechanism may be provided within the cartridge to keep the disk from rattling about when the cartridge is outside of the disk drive system. The retaining mechanism is typically released when the cartridge is inserted into the drive with the result that the disk can move laterally within the cartridge by a significant amount and thus not be aligned with the conical surface of the centering member when a self-actuating disk clamping mechanism attemps to clamp the disk onto the spindle-drive.
It is therefore an object of the invention to provide an improved disk centering and clamping apparatus that will accommodate substantial latitude in the initial radial position of the disk when clamping occurs while at the same time insuring that the disk is accurately and precisely centered in its clamped position as is required by optical and magneto-optical disk drive systems.
It is another object of the invention to provide low cost, compact disk positioning and self-actuated clamping apparatus that quickly and reliably repositions and precisely centers a disk that may be substantially misaligned inside a protective cartridge upon insertion into the drive system.